A conventionally known heat exchanger includes a pair of headers facing each other horizontally in its upper and lower portions, a plurality of flat heat transfer tubes communicatively connected in parallel with the headers at uniform intervals, and corrugated fins provided in a gap between the flat heat transfer tubes to be brought into intimate contact with the tubes. The heat exchanger causes refrigerant that is a heat exchange medium to be distributed in parallel to the plurality of flat heat transfer tubes simultaneously.
When such a heat exchanger is subjected to a heating operation in cold weather as an air conditioner outdoor unit of heat pump type for cooling and heating, frost is formed on the fin and the surface of the heat transfer tube, decreasing a heat exchange efficiency.
Japanese Patent Laying-Open No. 09-280754 (PTD 1) discloses a heat exchanger to take a measure against such frost formation. The heat exchanger includes corrugated fins disposed to project windward from flat heat transfer tubes and includes louvers formed only in its leeward portion.